Google Pixel & Pixel XL
Google's Pixel and Pixel XL are extremely cheap and they're getting upgraded to Android Q later this year. Still, you're better off going with a newer Pixel phone (if that's what your set on doing) in 2019.
The Pixel and Pixel XL replaced the Nexus series several years ago and at one point they were two of the best smartphones on the market. Now, not so much.
While they can still hold their own, their hardware is extremely outdated, particularly the cameras. If you love shooting photos and video on your phone you'll without a doubt want to go with a newer Pixel model.
And thanks to the rest of their hardware, they're going to outperform the original Pixels in key areas like battery life, overall speed, and gaming.
Software support for the original Pixel and Pixel XL will end much sooner as well. So if you're planning to hold onto your next phone for awhile, and you don't want to rely on the development community, you'll want to go with a newer model.